The axle bending gets done between the spring and the spindle- - - - -NEVER in the middle! I use a piece of 8 or 10 inch I-beam at least as wide as the axle, and a foot or so beyond each tire is better. Chain the spring mount area to the I beam with several wraps of proof coil chain, then fabricate a support a foot or so inboard of the spring mount between the I beam and the axle. A piece of 3 inch square tubing works well for that. Put the bottle jack under the kingpin area, and jack it up until you can see the angle change a little. Go slightly beyond the amount you want the camber to change, as it will rebound somewhat. To increase the positive camber reverse the process- - - -chain the spindle area down, and jack up at the spring support area.
Better idea- - - - -get a pro to do the bending- - - - -when a 20-ton jack comes loose during the bending operation, it flies across the shop and takes concrete blocks out of the wall! Don't get in its way!
Jerry